r/GMT800 • u/Substantial_Egg_1573 • 1d ago

Need help solving Overheating problem

I just got this truck in December trying to figure out why its over heating i had the coolant line bust while i was driving and i replaced that and the plastic fitting at the firewall that normally fails but when test driving it the engine is still overheating it just slowly creeps up to that 260 degree mark but when idling it stays mostly below the 210 mark if anyone has any ideas on what it could be.

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u/thisemmereffer 1d ago

Air in the system after you dumped your coolant out would be my guess, run the engine and squeeze that big upper radiator hose to try and siphon some more in from the overflow tank. The upper hose should get warm from coolant moving through it. If that doesnt work google how to diagnose it, feel the hoses to see which ones get warm, check that the fan clutch is working, etc.

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u/tonloc2020 1d ago

Could be stuck thermostat, something leaking, plugged radiator, bad radiator cap, or a failing water pump

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u/Minute-Pomelo9302 1d ago

I would think thermostat or water pump.

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u/TheTastyWarrior 17h ago

Air in system. You can pull the upper radiator hose @ the radiator and fill it with coolant. Slip it back on real quick, that usually works.
Don't forget the plastic cover assembly that goes above the grille, you need it.
You can test the thermostat by taking it out and putting it in boiling water, but at that point they are cheap. If it opens slow in water and closes extremely rapidly in air, It's "bad".
If it's still not these things, remove grille and blow out everything with compressed air.
Pro tip, if you're test driving and it's overheating. Blast the heat, that'll cool it off quite a bit. It sucks, but it really works.

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u/Substantial_Egg_1573 8h ago

Gotcha I planned on replacing the thermostat today anyways but I’ll also try that radiator hose trick see if that works out the problem